Many electronic apparatus include input devices for inputting data. Input devices of, for example, a mobile phone, a desktop or a notebook, usually have several input modes, for example, English input mode, Chinese input mode and numeral input mode. Because users often are not aware of the current input mode when they input data, erroneous input or lowering of input speed occurs from time to time. Therefore, there is a need to provide input devices allowing users to quickly differentiate between the input states.